The outrage was quickly and neatly carried through. Just before nine o'clock on the evening of Thursday 3 April, 1913, when Manchester Art Gallery was due to close and few people were about, an attendant heard "crackings of glass" coming from one of the galleries. Two attendants ran into the gallery and found three women, Lillian Forrester, Annie Briggs and Evelyn Manesta, running round, breaking the glass of the biggest and most valuable pictures in the collections. It had been well planned. Nowhere else in the gallery were hung so many famous paintings so close together. The gallery doors were shut by the doorkeeper and the three women were caught.

There was a hammer on the gallery floor. The hammer had a card tied to it with the coloured ribbons of the Women's Social and Political Union (WSPU). One side of the card bore the message "Parliament for dishonourable men; prison for honourable women." The other side of the card read: "Stop forcible feeding."

The Manchester Art Gallery is celebrating the centenary of the picture-smashing with a series of exhibitions and events called Wonder Women. This includes a fascinating video interview, available online, recorded in 1978, with Elizabeth Dean, a working-class Manchester suffragette involved in active protest. She tells how she "danced with temper" when she heard Asquith's proposal for limited suffrage.

Since 1909 the WSPU had become increasingly militant. Parliament wasn't listening to their arguments. Promises for debate and for reform had been broken again and again. Votes for women was caricatured in the press as a joke or an irritation. The Anti-Suffrage League had established 26 offices up and down the country – mostly staffed by women. Pankhurst made a call to arms: Deeds not Words. At the Manchester trial for "malicious damage" the accused women objected to the word "malicious". Annie Briggs told the judge: "This is not a personal but a world question. Women have to protest against things which are intolerable to them."

Her voice sounds modern. It is modern. "Death to Prison, Freedom to Protest" is the Pussy Riot version that landed two of the band members in prison. (At the suffragettes' trial the sentencing judge told the women: "If the law would allow I would send you across the world in a sailing ship as the best thing for you.") The head of the Russian Orthodox church, Patriarch Kirill, sided with Putin, whose presidency he called "a miracle from God", to denounce Pussy Riot as degenerate hooligans. He insisted that no one should get away with activism at a shrine, forgetting, I suppose, that Christ did physical damage to the tables set up in the temple by the money-changers. Hypocrisy and moral outrage are useful drillbits in the toolkit of oppression. The easiest way to run a hole through arguments about social justice is to denounce the activists as enemies of the people. The Pankhursts and Pussy Riot were both accused of attacks on moral values and public property: the museum and the church. The property standing as the physical symbol of the establishment.

The suffragette composer Ethel Smyth – also imprisoned, in Holloway – saw it differently. "There is something hateful, sickening in this heaping up of art treasures, this sentimentalising over the beautiful, while the desecration and ruin of bodies of women and little children by lust, disease, and poverty are looked upon with indifference."

Pankhurst pointed out to the judge at her trial that the legal system allowed a maximum sentence of 14 years for her "crime" of incitement to violence. The maximum penalty for child-rape was two years. Pussy Riot's prosecution document ran to more than 2,800 pages, even though they had protested in front of an altar for less than a minute. Pussy Riot went on hunger strike in protest at their sham trial and sham justice. The suffragettes had been hunger striking since 1909. That note on the other side of the hammer, "Stop forcible feeding", was an attempt to draw public attention to what was happening to women prisoners in Holloway.

The prisoner was held fast while a rubber tube was pushed into her nose or throat and a warm vomit-like concoction of broth poured in through a funnel. Women choked on the muddy puree, or threw up. The further a woman opened her mouth, as she gasped for air against the suffocating mess pressing on her lungs, the deeper the tube was rammed down her throat. Jaw bruising, broken teeth and noses, swollen tongues and throat infections were routine. There was also the fear of contaminated mucus infection from other prisoners as the tubes were shared.

Pankhurst wrote of her time in Holloway: "Sickening scenes of violence took place almost every hour of the day as the doctors went from cell to cell performing their hideous office. I shall never while I live forget the suffering I experienced."

In 1914 the writer Djuna Barnes, author of the 20th-century classic Nightwood, wrote an article called "How It Feels to Be Forcibly Fed". She submitted herself to the practice so that she could write in support of the suffragettes.

Force-feeding was legal. Unlike smashing the glass on pictures. With the exquisite irony of the torturer, the government did discontinue force-feeding – the label on the hammer did its job – only to replace it in 1913 with one of the nastiest of the hasty little laws passed to make a mock and a misery of women's protest: the Prisoners (Temporary Discharge of Ill Health) Act. Known as the Cat and Mouse Act, it was well named. It allowed women on hunger strike to leave prison when their health was in peril. As soon as they had recovered they were rearrested.

Protest movements make common cause across class, and it was one of the achievements of the WSPU that women whose lives were strictly segregated in the rigid class apartheid of Edwardian England were able to come together to stand shoulder to shoulder against the women (and men) of every class who opposed a politics of equality.

Too much has been made of the splits, frictions and fights among the suffragettes. That's what happens in active protest. What should be celebrated is the fact that our great-great-grandmothers changed the world – whether they were washerwomen or women with private means. I am sure that the partial enfranchisement of women in 1918 was designed to fracture the solidarity that women had formed across class, both during the protest years and the war years. Women working side by side in factories and on farms, in shops, driving vehicles, staffing hospitals and schools, posed a brand new threat to the post-war male elite. Divide and rule was the reasoning behind the Representation of the People Act 1918 that gave votes to women over 30, provided they were householders or married to householders, or owned property, or were graduates in a university constituency. Working women had risked more and been punished more severely than their better-off sisters. In 1918 they were pushed aside.

One of the Pussy Rioters has had her sentence commuted while her sisters remain in the "gulag", their appeals thrown out. Already there is open bitterness and feelings of betrayal. For women in easier circumstances in the west, at home or at work, the not-so-subtle message is that feminists are ballbreakers but real women are babes. We're all equal now – get over it – is the mantra whenever women stand up against Page 3, against unequal pay, against institutional sexism, against the sunny one-sided world of positive discrimination for men known as a level playing field.

I was in the States recently watching wall-to-wall coverage of Facebook chief operating officer Sheryl Sandberg and her new book Lean In – a success manual for women. Only 4% of women in land-of-opportunity America are at board level. Sandberg is doing her best but maybe direct action is what is needed. Radicalism for women may mean more than political argument. The anarchist group Femen, who protest with bare breasts, call themselves topless warriors, reclaiming the body and simultaneously using it as a weapon of war against patriarchy. They receive death threats daily and have had to flee from Ukraine since chain-sawing down a cross in Kiev on the day of the Pussy Riot verdict.

Revisionist history teaches that women got the vote by "proving" their competence during the first world war. Competence was a touchy subject. Titanic had gone down in 1912 thanks to the negligence of Captain Smith – and two weeks before Titanic sank, Captain Scott's manly incompetence had left him dead in Antarctica.

The day after Titanic sank the British press did not report a remarkable feat: an American screenwriter called Harriet Quimby flew her own plane across the Channel. The water-logged and frozen hierarchies of empire were being challenged by the possibility of a lighter, airborne world, where women would be equal partners in a new democracy. The fight had nothing to do with competence, everything to do with sexism. Captain Scott and Captain Smith both had statues cast in honour of their "heroism". To this day there is no statue of Emmeline Pankhurst in Manchester.

At the outbreak of war Pankhurst ordered all campaigning to cease. The WSPU threw its considerable organisational network into the war effort.

The suffragettes believed that a woman who could vote was a woman who could change the way society operated. That hasn't happened. Instead women have become adapters to an environment that doesn't suit us. Men control the workplace and the work ethic. Now that our brain power cannot be doubted our bodies have been requisitioned. When a woman cannot feel comfortable in her own body she has no home.

There are a billion illiterate people in the world; two-thirds of them are women. We are not equal. Some of us do far better than others in terms of reward and power. All of us owe a debt to those women of every class who risked so much for us 100 years ago, and we owe women like Pussy Riot a debt too. When young women with children can be sent to prison by a gang of powerful men, feminism needs to find the power of NO.